1) Field of the Invention
The present invention relates to a microscopic illumination apparatus.
2) Description of Related Art
FIG. 1 is a schematic configuration diagram that shows one configuration example of the microscopic transmitting illumination apparatus conventionally used in common.
The conventional microscopic illumination apparatus as shown in FIG. 1 is provided with: a lamp house 1 having a light source 2 and a collector lens 3 for converting a beam of divergent rays emanating from the light source 2 into a beam of substantially parallel rays; a field stop 4 disposed at a position conjugate with an illumination target surface 8 for regulating an illuminated area; and a field lens 5 for converting the beam of substantially parallel rays from the lamp house 1 into a beam of convergent rays. Via the collector lens 3 and the field lens 5, the light source 2 is projected at a position of an aperture stop 6 disposed at an entrance-side focal position of a condenser lens 7. A specimen surface, as the illumination target surface 8, is illuminated via the condenser lens 7 with the light from the light source 1 converging on the aperture stop 6. The reference numeral 20 denotes a mirror. It is noted that, in the drawings included in the present application, showing the prior art or the present invention, like reference numerals are used to denote like elements or components.
The illumination optical system of the commonly used, conventional microscopic illumination apparatus as shown in FIG. 1 is disclosed, for example, in Japanese Patent Application Preliminary Publication No. Hei 08-101344.
In recent microscopy, specimens are often photographed via digital cameras, where as the digital cameras, which use sensors such as CCDs or CMOSs, are more sensitive to brightness variation than direct observation by human eyes or photographing by silver halide cameras. Therefore, in photographing via a digital camera, illumination unevenness, which should have not mattered under direct eye observation or photographing via a silver halide camera, is conspicuous. By this reason, for a microscope in which photographing is performed via a digital camera, the illumination system is increasingly required to achieve uniform illumination by precluding illumination unevenness as much as possible.
The illumination system shown in FIG. 1 as a configuration example is called Koeller illumination, which is configured to allow, theoretically, a specimen to be exposed to illumination free from uneven brightness. In practice, however, intensity distribution of light with respect to directions of rays emitted from the light source is not uniform, as shown in FIG. 2A. Consequently, intensity distribution of light with respect to distance from the optical axis in the plane A in the microscopic illumination apparatus shown in FIG. 1, for example, is non-uniform as shown in FIG. 2B and accordingly illumination unevenness occurs. If angular distribution of rays emitted from the light source could be made uniform, uniform illumination without uneven brightness would be achieved. However, this is difficult in practice. To solve this problem, as a measure for reducing illumination unevenness caused by angular distribution of rays emitted from a light source, there has been a conventional method in which an integrator typified by a fly-eye lens divides a beam of rays into multiple beams to be evenly used for illumination.
FIG. 3 is a schematic configuration diagram that shows a conventional example of the microscopic illumination apparatus in which an integrator is used. In this microscopic illumination apparatus, a beam of divergent rays from a light source 2 is converted into a beam of substantially parallel rays via a collector lens 3, to be incident on the integrator 9. The integrator 9 is arranged, via a projecting lens 10 and a field lens 5, to be in conjugate positional relationship with an aperture stop 6 disposed at an entrance-side focal position of a condenser lens 7. Rays incident on the integrator 9 are spread with a same aperture angle both at the optical axis and a region off the optical axis. Here, since the integrator 9 and the entrance-side focal position of the condenser lens 7 are in conjugate positional relationship, both of rays emergent from the axial position (drawn with broken lines) and rays emergent from an off-axis position (drawn with solid lines), on the integrator 9, illuminate a same range on the illumination target surface 8. Therefore, even if distribution of amount of light of the beam of substantially parallel rays is not uniform, uniform illumination without uneven brightness can be accomplished on the illumination target surface 8 upon the beam of rays being divided at the integrator 9 and each of the multiple beams as divided being dispersed. A microscopic illumination apparatus using an integrator as shown in FIG. 3 is disclosed, for example, in the Japanese Patent Application Preliminary Publication (KOKAI) No. 2002-6225. The reference numeral 20 denotes a mirror.